A system-on-a-chip (SoC) typically includes a number of different circuit blocks. For example, an SoC might include a SERDES, a phase-locked loop (PLL), an analog-to-digital converter (ADC), and so on. Such circuit blocks often require their own band-gap circuit to provide a band-gap reference signal that is independent of process, voltage, and temperature (PVT) variations. But providing a band-gap reference circuit for each circuit block is costly because each band-gap reference circuit demands its own off-chip resistor, die space, and power.
To save power and reduce costs, an alternative approach is to distribute the band-gap reference signal to circuit blocks from a common band-gap reference circuit. For example, in an open-loop architecture without repeaters, a band-gap reference circuit that is shared by a group of circuit blocks distributes its band-gap reference signal to the circuit blocks through corresponding traces or leads. But such an approach is plainly unsatisfactory for precise distribution of the band-gap reference signal since the amplitude of the band-gap reference signal received by each circuit block will vary depending upon the resistive loss in the corresponding lead. Due to this loss, those circuit blocks farther away on the die from the band-gap reference circuit will receive a weaker band-gap reference signal in contrast to those circuit blocks that are closer on the die to the common band-gap reference circuit. An open-loop architecture in which the band-gap reference current is distributed through a series of repeaters addresses this resistive loss in amplitude. In the series of current repeaters, the reference current is successively repeated from current repeater to subsequent current repeater. But each repeater introduces some level of error that then propagates down through the subsequent repeaters in the series. For example, if each repeater in a series of five repeaters introduces an error of 5% in its repeated band-gap reference signal, the repeated band-gap reference signal from the fifth and final repeater in the series may have an error of 27% from the original band-gap reference signal that was distributed from the common band-gap reference signal to the first repeater in the series.
To address the error that would otherwise build-up in a series of repeaters, it is known to feedback the repeated band-gap reference signal from the final repeater in a series of current repeaters to the band-gap current source that drives the band-gap reference current to a first current repeater in the series. The band-gap current source may then adjust the band-gap reference current responsive to the feedback so that the error at the final repeater is minimized. Such a feedback scheme may be denoted as a global feedback in that the feedback from the final current repeater applies to all the repeaters in the series. But this use of global feedback does not control the local error at the various repeaters in the series prior to the final current repeater. For example, it may be that the error is unacceptably high for current repeaters in the middle of the series despite the error for the final current repeater being controlled through the global feedback to the band-gap reference circuit.
There is thus a need in the art for improved band-gap reference signal distribution architectures.